There is a substantial amount of evidence which indicates that many of the actions of prostaglandins in the E series (PGE) are different from those in the F series (PGF). These differences are particularly notable in arterial and bronchial smooth muscle which are known to be relaxed by PGE and constricted by PGF. In light of these different physiologic effects, we plan to synthesize compounds which have the potential for inhibiting the reductase or isomerase component enzymes of the prostaglandin synthetase system in an effort to obtain agents which will selectively inhibit biosynthesis of PGF or of PGE. The design rationale for the proposed inhibitors in based on the knowledge than an endoperoxide is a precursor in the biosynthesis of PGE and PGF. Such selective inhibitors would be useful as pharmacologic tools in investigating the actions of prostaglandins. Moreover, particular attention will be focused on the development of compounds which inhibit PGF and not PGE, as these may be useful as antihypertensives and antiasthmatics.